The present invention relates to battery technology, and more particularly to a microbattery structure for providing hermatically sealed microbatteries.
There exists a range of emerging applications (e.g., biomedical, IoT, remote sensing) where very small, low-profile power sources, on the order of 100 μAh capacity or less, are required. While functional batteries of this size are relatively simple to fabricate, the requirements of small physical dimension and low profile (far less than any existing metal coin cell battery on the market today) make it quite difficult to fully and hermetically seal such batteries. Typically, metal cans or coin cells are of cylindrical symmetry and employ a crimped seal between the outer metal and a polymer gasket, but such crimped seals are extremely difficult or impossible to make if the entire cell is 1 mm or less in width, 0.2 mm thick and of an arbitrary shape, e.g., rectangular or arc-shaped.
Typical flexible battery structures, which do not use metal cans, but rather flexible polymer enclosures, are often the size of a postage stamp, and require very large sealing zones at their edges, on the order of several millimeters wide. If these polymer/adhesive seals were much narrower, the seal lifetime would be considerably impacted. In such systems, it would be highly impractical to attempt to create a seal width of much less than 1 mm. As such, a serious sealing problem arises when trying to fabricate very small, thin, narrow batteries of 1 mm total width or less.
Existing commercial solutions are either metal can type packages of cylindrical symmetry with crimped seals, or flexible polymer packages with very wide seal widths of several millimeters. Certain long-life lithium ion batteries employ glass-to-metal seals to ensure full hermeticity since Li cannot be exposed to any moisture. However, given the constraints of the very small physical dimensions given above, and the desire for a non-Li battery chemistry such as the MnO2—Zn system with an alkaline or acidic electrolyte, very few packaging options exist for creating a quality seal of 100 μm width or less.
U.S. Pat. No. 6,432,577 B1 to Shul et al. discloses a method and apparatus to fabricate a microbattery that uses silicon as a structural component, packaging component and semiconductor. The method disclosed by Shul et al. uses four silicon wafers to form a planar microbattery structure in which two silicon wafers serve as structural frames and two silicon wafers serve as an anode and a cathode, respectively. The external silicon frames are of 425 μm thickness each. Shul et al. use an epoxy sealant material to bond the two external silicon frames together. This technique employs an O-ring to bond the two silicon wafers together with epoxy material to form a hermetic seal. Use of O-ring increases the seal width substantially.